#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;

int main()
{
	string s1;
	cout << s1 << endl;

	string s2("hello world");
	cout << s2 << endl;

	string s3("hello world", 6, 5);
	cout << s3 << endl;

	string s4(s2, 0, 5);
	cout << s4 << endl;

	string s5("aaaaaaa");
	cout << s5 << endl;

	string s6(10, 'a');
	cout << s6 << endl;

	string s7("hello world", 10);
	cout << s7 << endl;
	return 0;
}